Chapter 14- Acid-Base Balance and ABGs (editing)

What is pH a measure of?

measure of hydrogen ion concentration

Acids

Release hydrogen ions (H⁺) when dissolved in water.

Bases

Accept hydrogen ions (H⁺) or release hydroxide ions (OH⁻).

What does acid/base strength tell you?

Strength refers to how completely an acid or base dissociates (ionizes) in water.

Acidosis

A process that causes blood pH to decrease (too much acid or too little base).

Alkalosis

A process that causes blood pH to increase (too much base or too little acid).

Acidemia

Actual ↓ pH in blood (pH < 7.35).

Alkalemia

Actual ↑ pH in blood (pH > 7.45)

What is the body's first line of defense against pH change?

Buffer Systems

The chemical buffer system is based on the balance between which weak acid and which weak base?

Carbonic acid (H2CO3) - weak acid

Bicarbonate (HCO3) - weak base

How do buffers work?

Buffers work by binding free H⁺ ions when pH drops or releasing H⁺ ions when pH rises

Neutralization

A reaction between an acid and a base, forming water + salt.

What are the 3 primary mechanisms for pH regulation in the body?

• Chemical buffer system

• The respiratory system

• The renal system

What does the chemical buffer system respond to?

Responds to changes in the hydrogen ion concentration in the blood.

How does the respiratory system respond to pH changes?

Regulates the levels of PCO2 in the blood.

How does the renal system respond to pH changes?

Regulates the levels of HCO3− in the body.

Name the pH mechanism described:

-First Line of defense

-Carbonic Acid, Phosphate, and Protein buffer systems

-Immediate Response (seconds)

Chemical Buffer system

Name the pH mechanism described:

-The most effective

-Filters and eliminates nonvolatile acids from the body via urine

-Slowest, up to 24+ hours response time

Renal system

Name the pH mechanism described:

-Two times the buffering power all systems combined

-Eliminates Volatile Acids from the lungs

-1-3 minutes for response

Respiratory system

A weak acid controlled by the lungs through CO₂ removal.

Carbonic Acid

A weak base controlled by the kidneys through reabsorption or excretion.

Bicarbonate (HCO₃⁻)

Normal blood ratio of HCO₃⁻ to H₂CO₃

20:1, which keeps pH around 7.4.

What are the 3 chemical buffer systems?

• Carbonic Acid buffer system

• Phosphate buffer system

• Protein buffer system

Which chemical buffer system regulates pH mainly in the ECF (blood)?

Carbonic acid buffer system

Which chemical buffer system is active mainly in the ICF and renal tubules?

Phosphate buffer system

Which chemical buffer system is active in both the ICF and ECF spaces?

Protein buffer system

Which chemical buffer system accounts for two-thirds of the buffering power of the blood?

Phosphate buffer system

How does the phosphate buffer system work?

Works by exchanging H+ ions with sodium phosphate (Na2HPO4) to resist large pH changes.

What is the most important chemical buffer system in the body?

Carbonic Acid-Bicarbonate buffer system

What is the reaction that the Carbonic Acid-Bicarbonate buffer system relies on?

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

H₂CO₃

carbonic acid

Where is carbonic acid controlled in the body?

Lungs controlled by changes in ventilation

Where is bicarbonate controlled in the body?

Kidneys controlled through reabsorption or excretion

What happens when CO2 increases in the carbonic acid-bicarbonate buffer system?

Carbonic acid increases which increases H+ ions and decreases pH (acidosis)

What is the most important protein buffer in the blood?

Hemoglobin (Hb)

-It binds CO₂ and H⁺ in tissues and releases CO₂ in the lungs

What is known as the "respiratory acid"?

CO₂, which when dissolved in water forms carbonic acid (H₂CO₃).

What are the effects of hypoventilation? What does it cause?

Leads to ↑ CO₂ ,↑ H₂CO₃, ↑ H⁺, ↓ pH

Causes Respiratory Acidosis

Hyperventilation

Leads to ↓ CO₂, ↓ H₂CO₃, ↓ H⁺, ↑ pH

Causes Respiratory Alkalosis

Which chemical buffer system accounts for two-thirds of the buffering power of the blood and within the cells?

Phosphate Buffer System

Central and peripheral chemoreceptors function

Monitor arterial PCO₂ and send feedback to the medulla to adjust breathing rate and depth

Chemical buffers

Act within seconds to neutralize excess acids or bases

Which system has two times the buffering power of all chemical systems combined?

The respiratory system

Which system has the slowest response time?

The renal system has the slowest response time, up to 24+ hours.

Which electrolyte works by exchanging H⁺ ions to resist large pH changes in the phosphate buffer system?

Sodium phosphate (Na₂HPO₄)

Phosphate Buffer System equation

Na₂HPO₄ + H⁺ ⇌ NaH₂PO₄ + Na⁺

Donates H⁺ when pH rises in the protein buffer system

Carboxyl group (-COOH)

Binds H⁺ when pH drops in the protein buffer system

Amino group (-NH₂)

Condition characterized by increased CO₂ and decreased pH, with kidneys increasing HCO₃⁻ reabsorption.

Respiratory Acidosis

Condition characterized by decreased CO₂ and increased pH, with kidneys decreasing HCO₃⁻ reabsorption.

Respiratory Alkalosis

Condition characterized by decreased HCO₃⁻ and decreased pH, with lungs increasing ventilation to decrease CO₂.

Metabolic Acidosis

Condition characterized by increased HCO₃⁻ and increased pH, with lungs decreasing ventilation to increase CO₂.

Metabolic Alkalosis

Regulates blood pH by excreting hydrogen ions (H⁺) into urine and reabsorbing or generating bicarbonate (HCO₃⁻) into the blood.

Kidneys Regulation of pH

Kidneys Regulation of pH:

Regulates blood pH by excreting ___________ into urine and reabsorbing or generating ___________ into the blood.

1. hydrogen ions (H⁺)

2. bicarbonate (HCO₃⁻)

Conditions where the lungs and kidneys respond to alterations in pH, categorized as uncompensated or compensated.

Acid-Base Disturbances

When the body responds to a change in the acid-base status.

Compensated

When the body has not responded to a change in the acid-base level.

Uncompensated

How will the kidneys respond to acidic blood?

Kidneys retain HCO₃⁻ and excrete H⁺ into urine, increasing blood pH toward normal.

How will the kidneys respond to alkaline blood?

Kidneys excrete HCO₃⁻ into urine and retain H⁺, decreasing blood pH toward normal.

Common Causes of Respiratory Acidosis

COPD, hypoventilation, drug overdose.

Common Causes of Respiratory Alkalosis

Anxiety, pain, hyperventilation, fever.

Common Causes of Metabolic Acidosis

DKA, diarrhea, renal failure, aspirin overdose

Common Causes of Metabolic Alkalosis

Vomiting, diuretics, corticosteroids, hypokalemia

Fixed Acids removed by Kidneys

Lactic acid, phosphoric acid, ketoacids, uric acid.

Primary Change in Metabolic Alkalosis

↑ HCO₃⁻

Primary Change in Metabolic Acidosis

↓ HCO₃⁻

Compensation in Metabolic Alkalosis

Lungs decrease ventilation to retain CO₂ and lower pH

Compensation in Metabolic Acidosis

Lungs increase ventilation (Kussmaul respirations) to blow off CO₂ and raise pH

Mixed Acid-Base Disorders

Occurs when two or more primary imbalances happen at the same time

Arterial Blood Gases (ABGs)

A laboratory test that measures how well the lungs and body maintain acid-base balance and oxygenation

Normal Range for pH

7.35 - 7.45

Normal Range for PaCO₂

35 - 45 mmHg

Normal Range for HCO₃⁻

22 - 26 mEq/L

Normal Range for PaO₂

80 - 100 mmHg

Normal Range for SaO₂

95 - 100%

Normal Range for Base Excess (BE)

-2 to +2 mEq/L

ABG vs. VBG vs. CBG

ABG → gold standard for assessing ventilation and oxygenation; VBG → useful for trending CO₂ or pH changes but not accurate for PaO₂; CBG → primarily used in NICU or pediatric settings where arterial sampling is difficult